Method of beneficiating feldspar



United States Patent METHOD OF BENEFICIATING FELDSPAR James E. Lawyer, Lakewood, Colo, assignor to International Minerals & Chemical Corporation, a corporation of New York No Drawing. Application November 8, 1955, Serial No. 545,805

9 Claims. (Cl. 209127) This invention relates generally to the beneficiation of non-metallic minerals. More particularly, it relates to the beneficiation of non-metallic silicates. Still more particularly, it relates to the electrostatic benefication of feldspathic rock minerals, i. e., silicates of aluminum with sodium, potassium and sometimes calcium.

It has long been known that it is possible to beneficiate minerals by electrostatic methods. These methods are based upon a variety of different methods of operation, although all are determined electrostatic separations. The most common process receiving commercial acceptance has been the so-called electrostatic roll separation based upon differences in surface conductivity of chemically dissimilar materials.

In this type of separation a charge is imparted to the material to be separated as it contacts the electrostatic roll. The speed with which the charge is transferred to the roll determines when the particles are free to fall off and thus separated from material which continues to be pinned to the roll so long as it remains charged and not brushed off. When materials do not naturally have differences in surface conductivity, this characteristic may be altered by the use of preferential surface wetting reagents in a manner similar to reagentizing in flotation operations. Reagents are preferentially selective onlyfor rather specific ores and even where effective materially raise the cost of producing a marketable product.

A few metallic minerals have been shown to be electrostatically separable when the particles are passed as freely falling bodies between oppositely charged elec' trodes. In order to precondition or charge the materials to be separated, the material in this type of operation is subjected to a frictional or Wiping action against a grounded metallic conductor. While separations have been proven feasible, this type of operation has to date never been considered economical or commercially acceptable.

Now it has'been discovered that feld's'pathic' rock matcrials or minerals can be beneficiated and feldspar separated from gangue and/or different chemical feldspar specie by utilizing the free fall type of electrostatic sep-- aration under proper operating conditions. This separation can be effected on comminuted ore without the addition of expensive preferential surface Wetting agents or chemical reactants.

It isa primary object of this invention to overcome the disadvantages and shortcomings of processes heretofore muse.

It is another object. of this invention} to provide an "ice It is still another object of this invention to provide an electrostatic method for separation of the feldspars from gangue material, such as quartz.

It is a still further object of this invention to provide a method of separating feldspathic rock materials wherein the comminuted ore in its natural state is charged and the charged material separated as freely falling bodies between oppositely charged electrodes.

It is a further object of this invention to provide a method for the beneficiation of feldspar in air ambient wherein the particles even though they have conducitivity of approximately the same order of magnitude, nevertheless can be induced to accept electrical charges of sufiicient differences in magnitude and/or polarity to permit an electrostatic field to alter the free fall path of the particles and to permit accumulation of similarly electrified particles adjacent to one or the other of the electrodes.

These objects, as well as other objects of the invention which will become apparent upon a clearer understanding of the same, as set forth, may be accomplished by comminuting feldspathic rock sufficiently to substantially liberate the desired values from the gangue'. The comminuted ore is then dried and treated to develop electrical charges upon the ore particles. The comminuted ore is heated to a temperature within a predetermined range and maintained at such an elevated temperature until dry, during or subsequent to which a charged particle exchange is caused to take place in such fashion that differential charges are developed upon the ore particles whereby the charged particles are rendered responsive to an electrostatic field of a nature subsequently to be described.

Ore particles possess the ability to effect charged particle exchange by any of several different means and thereby acquire differential electrical charges. This difierential charge may be acquired by rupture of an electrical double area by mechanical forces, as for example, from interparticle' contact or by transfer of electrons from a source external to the ore components themselves. This differential charge can be markedly increased by agitation" of a proper character or by contacting the ore particles with an unlimited source of free electrons such as is made available by indicating a donor or acceptor'element which will be contacted by the ore particles, to the earth by an electrical conductor or a combination of these effects.

Temperature of the solids at the time of differential charging has a marked effect upon the character of the charge acquired. Feldspar ores acquire a markedability to become charged when heated to a temperature of between about F. and about 750 F. Heating is generally carried into a preferred range of between about 300 F. and about 500 F. The effect of this heating is evidenced by the increase in K20 value of the concentrate and also the improved recovery of K20 values in a valuable concentrate when the comparison is made between the variations accomplished after heating to the preferred range as compared to that of say approximately 200 F. While reference is made to ores, it will be understood that materials prepared by hand picking or other concentrating methods may likewise be treated in accordance with this invention.

Drying ofthe feldspar ore may be either by direct heating with gases containing products of combustion or byindirect methods of heating such as hot air or electric heating. Drying may be carried out by suspending the comminuted solids in hot drying gases or in tunnel type dryers and the like. j

The efliciency of the instant novel process is to a de gree dependent upon the particle size of comminuted ore. The most satisfactory particle size range for feldspar 3 beneficiation, from an economic standpoint, is that obtained by grinding a substantially dry feldspar ore so that approximately 100% of the comminuted ore is of a size between about 4 mesh and about 200 mesh, most of the comminuted ore preferably being between about 20 mesh and about 100 mesh size.

In. the instant process it is desirable to employ an apparatus which will minimize the possibility of altering the previously described charge with corona discharge or induction charging such as is employed in substantially all conductivity electrostatic separators. The electrodes should be kept at a high direct voltage potential substantially free of alternating current components.

The surfaces of either or both of the electrodes are positioned or formed at an angle to the path of flow of the undiverted material. This arrangement of electrodes is for the purpose of making the angle of divergency as wide as possible thus making the ultimate separation of materials with dividers more readily accomplished.

The strength of the electrostatic field which \villeffectively alter the path of ore particles varies with the average particle size and the type of material. The field gradient may vary from 1,000 to about 5,000 volts per inch of distance between electrodes in separating materials of relatively fine particle size and from 3,000 to 15,000 volts per inch for beneficiating of coarser particles. In all such discussion of field strengthit must be borne in mind that corona discharges which ionize air are to be avoided. In general, it is preferred to operate with a total impressed difference of potential in the range of about 30,000 volts to about 250,000 volts. Electrodes should be charged to this potential difference by means of a power supply substantially free of alternating current components, i. e., filtered DC. current low in so-called A. C. ripple. A steady supply of D. C. voltage may also be obtained without expensive filtering apparatus by the use of such equipment as rectified radio frequency power supply.

Theinvention may be further understood from a-'description of the processing operations. Feldspar ore which may be a pegmatite or a granite, is subjected to a grinding process in order to substantially liberate the feldspar values from the gangue comprising essentially quartz. The ground material is subjected to a screening operation generally to a size of -24 mesh, the coarse material of +24 mesh being recycled tothe grinding process. The fines are subjected to a separation, for example, an air separation. The coarse material of substantially -24 +200 mesh size is subjected to a second fines separation and the combined fines sent to discard. The coarse material of -24 +200 mesh size is fed directly to the separation process or to a surge bin. From the surge bin, material as needed is fed toa heater. Itis preferred, though not essential, to avoid an open flame as a direct source of heat for the comminuted ore, since this would tend to produce an environment of positive ions which would result in at least partial neutralization of the developed negative charge on the gangue.

The .ore particles are charged, whileheated to be tween about 150 F. to about 550 F., by being subjected for example, to a substantially horizontal shaking action in a grounded feeder such as a Syntron.

The temperature of the ore must not be allowed to drop appreciably before separation, particularly if heating in the low end of the temperature range of about 150 to 250 F. because the charge on the gangue material falls off appreciably to the detriment of the separation.

The charged ore is then subjected to the electrostatic field created by the electrostatic separator. If the ore is maintained in a dry condition such as was obtained as a result of the aforesaid heating, it may be cooled without seriously effecting the quality of the separation, but preferably the material is maintained for separation 4 within the temperature range of about 200 F. to about 300 F.

Upon passage into the electrostatic field, separation generally is effected to produce a feldspar concentrate, a middling fraction, and a quartz tailing fraction. The middling fraction is recycled to the heater. The amount of middling fraction, the same being a continuously Cit culating load, is dependent upon the grade of the. feed material and the amount of middling that the operator deems it economic to carry. Since the middling recycle operation is a closed circuit, in starting the separation process, the middling circuit must be filled before the equilibrium between the amount of feed material introduced and the amount of product and tails removed is reached. The middling fraction may be resubjected to electrostatic separation without repassage through the heater, if the particle surfaces have been maintained in a dry condition.

The tailing fraction is subjected to a scavenger clectrostatic separation where tailings and a feldspar concentrate are obtained. The feldspar concentrate having a concentration approximately equal to that of the fee is sent to the heater. The final tails are sent to waste.

The electrostatic field for separation is preferably created by employing at least two pairs of stationary, smooth, curved surface electrodes, one electrode of each pair being oppositively charged, the vertically adjacent electrodes bearing the opposite charge. The paired electrodes are usually secured with the smooth, convex surfaces of the electrodes opposite. The field gradient may vary considerably. However, it has een found that in the aforementioned process, between about 6,000 and about 15,000 volts per inch is a satisfactory commercial field gradient.

The following examples are given to illustrate specific applications of the instant process and are not to be construed as limiting the invention thereto.

EXAMPLE I A 1,000 pound sample of Connecticut feldspar pegrnatite was comminuted and airsized to produce an electrostatic feed material of -28 +200 mesh. This feed material was heated in a tray dryer to 500 F. to dry the ore. The heated ore was held at 500 F. for .30 minutes.

The hot ore then was delivered to a feed hopper from which the electrostatic feed material was delivered between the electrodes defining the electrostatic field by means of a vibratory trough in which the particles become charged. The timing of delivery was such that the trough fed material at the rate of 1,000 pounds per hour per foot of horizontal electrode length and at a temperature of 240 F.

The charged material passed as free falling bodies between vertical electrodes. The electrodes consisted of a spaced row of three inch diameter tubes arranged with approximately 1 inch of space between said tubes. The tubes were straight for approximately 6 feet of their vertical length and then curved smoothly on a radius of curvature of about 10 feet so that the bottom end of the tubes were approximately 18 inches further apart than the straight sections of said electrodes. The electrodes were spaced approximately 10 inches apart over their perpendicular length. The voltage impressed upon the elec trodes was approximately 90,000 volts giving a field gradient of approximately 9,000 volts per inch. Analysis of the feed and the products obtained by one pass through an electrostatic field:

Feed Concentrate Tall Weight, K20, Weight, K20, Weight, K10, Percent Percent Percent Percent Percent Percent EXAMPLE II Maine feldspar was comminuted and sized to produce an electrostatic feed material of approximately -8 +100 mesh. This feed material was heated in a baflile heat exchanger to approximately 300 F.

The hot ore was then delivered to a feed hopper from which electrostatic feed material was delivered between the electrodes defining the electrostatic field by means of a vibratory trough in which the particles become charged. The timing and delivery was such that the trough fed material at the rate of approximately. 500 pounds per hour per foot of horizontal electrode length and at a temperature of approximately 210 F. The voltage impressed upon the electrodes was approximately 90,000 volts, giving a field gradient of approximately 9,000 Volts per inch.

Analyses of the feed' and the products obtained by one. pass through an electrostatic field were as follows:

Calculated Percent Quartz Percent SiOe Percent Percent Percent N Pan 9.:

While in the above description it was shown that usually there are three products recovered out of a separation, i. e., concentrate, middling and tail, the above analysis shows greater separation to illustrate the segregation accomplished. In commercial operation, dividers usually are placed at the intersection of recovery bins, these dividers being movable to positions generally of the order of 45 from the vertical on either side thereof. Such dividers determine whether material of the character to be found in pan 4 for example would go into the concentrate bin or into the middling bin. Any combination of products having analyses between that shown for pan 1 and pan can be recovered as is desirable.

EXAMPLE III Connecticut feldspar was cone crushed and sized on a Sweco screen to recover a -14 mesh feed material. This sized material was heated to approximately 340 F. in an electrically heated oven. The heated material was transferred to the hopper of a Syntron feeder having a cast iron chute grounded to the earth by an electrical conductor. Material ran thru thus chute at a depth to give about /s inch at the discharge lip.

The contacted sample while within the temperature range of between 340 F. and 240 F. was fed to the electrostatic field at a rate of approximately 500 pounds per hour per linear foot of electrode width, the field gradiend being 10,000 volts per inch of distance separating the electrodes.

The results obtained utilizing a single pass through the electrostatic field are indicated by the following table:

Percent KzO/NazO Percent N 9.20

Percent Material Percent #1 Gone r minuting the feldspathic ore to a particle size of between about 4 and about 200 mesh to substantially liberate the feldspar values from the gangue, heating the comminuted feldspathic ore to a temperature of between 150 and 750 F., inducing the heated feldspathic ore particles without chemical pretreatment to accept differential charges while at a temperature of at least 150 F. and passing the differentially charged particles at a temperature of at least 150 F. into an electrostatic field to separate the feldspar from the gangue.

2. An electrostatic process for beneficiating feldspathic ore in its natural chemical state which comprises comminuting the feldspathic ore to a particle size of between about 4 and about 200 mesh to substantially liberate the feldspar values from the gangue, heating the comminuted feldspathic ore to a temperature of between 150 and 750 F., inducing the heated feldspathic ore particles without chemical pretreatment to accept differential charges while at a temperature of at least 150 F., passing the differentially charged particles at a temperature of at least 150 F. into an electrostatic field to separate the feldspar from the gangue, and recovering a feldspar concentrate characterized by a ratio of potassium spar to sodium spar substantially higher than that of the feed.

3. An electrostatic process for beneficiating feldspathic ore in its natural chemical state which comprises comminuting the feldspathic ore to a particle size of between about 20 and about mesh to substantially liberate the feldspar values from the gangue, heating the comminuted feldspathic ore to a temperature of between 300 and 500 F., inducing the heated feldspathic ore particles without chemical pretreatment to accept differential charges while at a temperature of at least F., and passing the differentially charged particles at a temperature of at least 150 F. into an electrostatic field to separate the feldspar from the gangue.

4. An electrostatic process for beneficiating feldspathic ore in its natural chemical state which comprises comminuting the feldspathic ore to a particle size of between about 4 and about 200 mesh to substantially liberate the feldspar values from the gangue, heating the cornminuted feldspathic ore to a temperature of between 300 and 500 F., inducing the heated feldspathic ore particles withoutchemical pretreatment to accept differential charges while at a temperature of at least 150 F., and passing the dilferentially charged particles at a temperature of between 200 and 300 F. into an electrostatic field to separate the feldspar from the gangue.

5. An electrostatic process for beneficiating feldspathic ore in its natural chemical state which comprises cornminuting the feldspathic ore to a particle size of between about 4 and about 200 mesh to substantially liberate the feldspar values from the gangue, heating the comminuted feldspathic ore to a temperature of between 150 and 750 F., inducing the heated feldspathic ore particles without chemical pretreatment to accept differential charges while at a temperature between 150 and 750 F., and passing the diiferentially charged particles at a temperature of at least 150 F. into an electrostatic field having a total impressed difference of potential of from about 30,000 to about 250,000 volts to separate the feldspar from the gangue.

6. An electrostatic process for beneficiating in its natural chemical state a feldspar ore comprising predominantly sodium and potassium spars and free quartz which comprises comminuting the feldspar ore to a particle size of between about 4 and about 200 mesh to substantially liberate the feldspar values from the quartz, heating the comminuted feldspar ore to a temperature of between 150 and 750 F., inducing the heated feldspar ore particles without chemical pretreatment to accept differential charges while at a temperature between 150 and 750 F., and passing the differentially charged particles at a temperature of at least 150 F. into an electrostatic field to separate the feldspar from the quartz.

7. An electrostatic process for beneficiating in its natural chemical state a feldspar ore comprising predominantly sodium and potassium spars and free quartz which comprises comminuting the feldspar ore to a particle size of between about 20 and about 100 mesh to substantially liberatelthe feldspar values from the quartz, heating the comrninuted feldspar ore to a temperature of between 300 and 500 F., agitating the heated feldspar ore particles without chemical pretreatment to develop diiferential charges thereon, passing the differentially charged particles at a temperature of at least 150 F. into an electro static field and separately collecting quartz, sodium feldspar and potassium feldspar concentrates.

8. An electrostatic process for benficiating in its natural chemical state a feldspar ore comprising prcdominantly sodium and potassium spars and free quartz which comprises cornminuting the feldspar ore to a particle size of between about 4 and about 200 mesh to substantially liberate the feldspar values from the quartz, heating the :comminuted feldspar ore to a temperature of between 300 and 500 F., inducing the heated feldspar ore par ticles without chemical pretreatment to accept dilferential charges while at a temperature of at least 150? F., passing the differentially charged particles at a temperature of at least 150 E. into an electrostatic field having a total impressed difference of potential of from about 30,000 to about 250,00 volts, and separately collecting quartz, sodium feldspar and potassium feldspar concentrates.

9. An electrostatic process for beneficiating feldspathic ore in its natural chemical state which comprises comminuting the feldspathic ore to a particle size of between about 4 and about 200 mesh to substantially liberate the feldspar values from the gangue, heating the comminuted feldspathic ore to a temperature of between 150 and 750 F., inducing the heated feldspathic ore particles without chemical treatment to accept ditferential charges while at a temperature between and 750 F., passing the diiferentially charged particles into an electrostatic field While at a temperature of at least 150 F., collecting a feldspar concentrate, a middling fraction and a tailing fraction, and recycling the middling fraction to the process. 1

References Cited in the tile of this patent UNITED STATES PATENTS OTHER REFERENCES Fraas et al.: Electrostatic separations of solids, Industrial and Engineering Chemistry, volume 32, No. 5, 600 605, May 1940.

Fraas et 211.: Contact potential in electrostatic separation, Bureau of Mines, R. l. 3667, November 1942.

Fraas et al;: An electrostatic separator for fine powders, Bureau of Mines, R. I. 3667, November 1942.

Frans et al.: The electrostatic separation of several industrial minerals, AIMME, Technical Publication No. 2408, July 1948.

Von Szantho: Electrostatic beneficiation in the industry of rocks and earths, Tonindustrie-Ztg und Keramische Rundschau, volume 77, 83-88 (1953).

Frans et 211.: Notes on drying for electrostatic separation of particles, American Institute of Mining and Metallurgical Engineers Technical Publication No. 2257, November 1947. 

1.AN ELECTROSTATIC PROCESS FOR BENEFICIATING FELDSPATHIC ORE IN ITS NATURAL CHEMICAL STATE WHICH COMPRISES COMMINUTING THE FELDSPATHIC ORE TO A PARTICLE SIZE OF BETWEEN ABOUT 4 AND ABOUT 200 MESH TO SUBSTANTIALLY LIBERATE THE FELDSPAR VALUES FROM THE GANGUE, HEATING THE COMMINUTED FELDSPATHIC ORE TO A TEMPERATURE OF BETWEEN 150* AND 750*F., INDUCING THE HEATED FELDSPATHIC ORE PARTICLES WITHOUT CHEMICAL PRETREATMENT TO ACCEPT DIFFERENTIAL CHARGES WHILE AT A TEMPERATURE OF AT LEAST 150*F. AND PASSING THE DIFFERENTIALLY CHARGED PARTICLES AT A TEMPERATURE OF AT LEAST 150*F. INTO AN ELECTROSTATIC FIELD TO SEPARATE THE FELDSPAR FROM THE GANGUE. 